US8534835B2 - Optical tomographic image photographing apparatus - Google Patents

Optical tomographic image photographing apparatus Download PDF

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Publication number
US8534835B2
US8534835B2 US13/034,147 US201113034147A US8534835B2 US 8534835 B2 US8534835 B2 US 8534835B2 US 201113034147 A US201113034147 A US 201113034147A US 8534835 B2 US8534835 B2 US 8534835B2
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tomographic image
optical
light
photographing apparatus
positional deviation
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US20110205490A1 (en
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Toshio Murata
Yukihiro Higuchi
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Nidek Co Ltd
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Nidek Co Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02015—Interferometers characterised by the beam path configuration
    • G01B9/02029—Combination with non-interferometric systems, i.e. for measuring the object
    • G01B9/0203—With imaging systems
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
    • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
    • A61B3/102—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for optical coherence tomography [OCT]
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02041—Interferometers characterised by particular imaging or detection techniques
    • G01B9/02044—Imaging in the frequency domain, e.g. by using a spectrometer
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
    • G01B9/02062—Active error reduction, i.e. varying with time
    • G01B9/02067—Active error reduction, i.e. varying with time by electronic control systems, i.e. using feedback acting on optics or light
    • G01B9/02068—Auto-alignment of optical elements
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02083—Interferometers characterised by particular signal processing and presentation
    • G01B9/02089—Displaying the signal, e.g. for user interaction
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/0209—Low-coherence interferometers
    • G01B9/02091—Tomographic interferometers, e.g. based on optical coherence

Definitions

  • An aspect of the invention is related to an optical tomographic image photographing apparatus for photographing a tomographic image of an object.
  • optical Coherence Tomography which has an interference optical system and photographs a tomographic image of an object.
  • the optical interference optical system of this apparatus splits a light flux emitted from a light source into a measurement light flux and a reference light flux.
  • This optical interference optical system guides the measurement light flux to an object, while guiding the reference light flux to a reference optical system.
  • the optical interference optical system combines the measurement light flux, reflected on the object, with the reference light flux, to obtain interference light, and thereafter makes a light receiving device receive this interference light.
  • This apparatus is used for, for example, obtaining a tomographic image of a living body such as an eyeball or skin.
  • This kind of apparatus also includes an apparatus which displays a tomographic image at a predetermined position on a display monitor by changing an optical path difference between a measurement light and a reference light at any time, even if the object moves while being photographed (refer to JP-A-2008-154939).
  • an optical-path-length varying member for example, a reference mirror
  • driving a motor in order to change the optical path difference.
  • a technical object of an aspect of the invention is to provide an optical tomographic image photographing apparatus which enhances the visibility of a tomographic image movie-displayed on a monitor.
  • the aspect of the invention includes the following configuration.
  • An optical tomographic image photographing apparatus for photographing a tomographic image of an object, includes: an interference optical system including: a measurement light source; and a splitter that splits light emitted from the measurement light source, such that the light is split in a measurement optical path for guiding part of the light to the object as measurement light and in a reference optical path for generating reference light, the interference optical system combining reflected light from the measurement optical path, the reflected light being obtained by reflection of the measurement light on the object, with the reference light from the reference optical path, to guide combined light to a detector; an optical scanner that is arranged in the measurement optical path for scanning the measurement light on the object; a driving part for moving an optical member arranged in the measurement optical path or the reference optical path in an optical-axis direction in order to adjust an optical path difference between the measurement optical path and the reference optical path; an image obtaining part that is connected to the detector for obtaining a tomographic image of the object based on a light receiving signal output from the detector; a monitor; and a control
  • the visibility of a tomographic image movie-displayed on a monitor is enhanced.
  • FIG. 1 is a view showing an optical system and a control system of an ophthalmic photographing apparatus of an embodiment of the invention
  • FIG. 2 is a view showing monitors on which a fundus front image and a fundus tomographic image are displayed;
  • FIG. 3 is a flow chart explaining a technique for correcting a display position of the fundus tomographic image
  • FIGS. 4A and 4B are schematic diagrams virtually illustrating a positional relationship between tomographic image data and a display region.
  • FIG. 5 is a view showing monitors on which a fundus front image and a fundus tomographic image which has been image processed are displayed.
  • FIG. 1 illustrates an optical system and a control system in an optical tomographic image photographing apparatus of an embodiment of the invention.
  • a fundus photographing apparatus as an example of an ophthalmic photographing apparatus will be described.
  • a description is given with a depth direction of an examinee's eye referred to as a Z-direction (direction of optical axis L 1 ), a horizontal direction referred to as an X-direction, and a vertical direction referred to as a Y-direction.
  • the optical system of this ophthalmic photographing apparatus is broadly divided into an interference optical system (hereinafter referred to as OCT optical system) 200 and a scanning laser ophthalmoscope (SLO) optical system 300 .
  • the OCT optical system 200 serves to obtain a tomographic image of a fundus of an examinee's eye E by use of an optical interference technique.
  • the SLO optical system 300 illuminates the fundus by use of infrared light, to obtain an SLO fundus image for observing the fundus.
  • each of the above optical systems has a light projecting optical system and a light receiving optical system, and is used as a photographing optical system for obtaining a photographed image of the eye.
  • the light projecting optical system projects at least part of light emitted from a light source to a predetermined region of the eye.
  • the photographing optical system receives reflected light from the predetermined region of the eye in a light receiving device.
  • the OCT optical system 200 there has been used an OCT optical system of a spectral domain type. Naturally, a time domain type (TD-OCT) or a swept source domain type (SS-OCT) may also be used. It is to be noted that the OCT optical system 200 and the SLO optical system 300 are incorporated in a housing (not illustrated). Further, this housing is three-dimensionally moved with respect to the eye E by a known (manual or electrically-powered) movement mechanism for alignment.
  • TD-OCT time domain type
  • SS-OCT swept source domain type
  • a dichroic mirror 40 is used as a light splitting member.
  • the dichroic mirror 40 makes a measurement optical axis L 2 of the OCT optical system 200 and a measurement optical axis L 1 of the SLO optical system 300 be the same axial.
  • the OCT optical system 200 splits a light flux emitted from the light source into a measurement light flux and a reference light flux. Further, the OCT optical system 200 guides the measurement light flux to a predetermined region of the eye (anterior segment or fundus), while guiding the reference light flux to the reference optical system. Subsequently, the OCT optical system 200 makes the light receiving device receive interference light obtained by combining the measurement light flux, reflected on the predetermined region of the eye, with the reference light flux.
  • the OCT light source 27 emits low coherent light.
  • a light source that emits light with a central wavelength of 840 nm and a band width of 50 nm (e.g., SLD light source).
  • a fiber coupler 26 serves as a light splitting member as well as a light coupling member.
  • the light emitted from the OCT light source 27 passes through an optical fiber 38 a as a guiding optical path, and is thereafter split by the coupler 26 into reference light and measurement light.
  • the measurement light travels toward the eye E via an optical fiber 38 b
  • the reference light travels toward a reference mirror 31 via an optical fiber 38 c.
  • an end 39 b of the optical fiber 38 b In an optical path for emitting the measurement light toward the eye E, an end 39 b of the optical fiber 38 b , a collimator lens 22 , a focusing lens 24 and a scanning part 23 are arranged.
  • the focusing lens 24 is movable in the optical-axis direction in line with a refraction error of the eye E for adjustment of a focus on the fundus.
  • the scanning part 23 is capable of scanning the fundus in XY directions with the measurement light.
  • This scanning part 23 includes two galvanometer mirrors, and is operated by driving of a scanning driving mechanism 51 .
  • the dichroic mirror 40 and an objective lens 10 serve as a light guiding optical system for guiding OCT measurement light from the OCT optical system 200 to the fundus.
  • the scanning part 23 of the embodiment arbitrarily adjusts a reflection angle of the measurement light by means of the two galvanometer mirrors. Hence a direction of scanning by means of the measurement light on the fundus is arbitrarily set. A tomographic image in an arbitrary area of the fundus is thus obtained.
  • the end 39 b of the optical fiber 38 b is arranged in a position conjugate with the fundus of the eye E.
  • the two galvanometer mirrors of the scanning part 23 are position arranged in a position substantially conjugate with a pupil of the eye E.
  • the galvanometer mirrors and the scanning driving mechanism 51 described above are used as an optical scanner (optical scanning part).
  • the optical scanner is arranged in the optical path for the measurement light flux (measurement optical path).
  • the optical scanner changes a traveling direction of the measurement light flux in order to scan the predetermined region of the eye in a transverse direction (XY directions) with the measurement light flux.
  • an acousto-optic device (AOM: Acousto-Optic Modulator) for changing a traveling (deflection) direction of light, and the like are used.
  • the measurement light emitted from the end 39 b of the optical fiber 38 b is collimated by the collimator lens 22 , and thereafter reaches the scanning part 23 via the focusing lens 24 .
  • the two galvanometer mirrors are driven, to change a reflecting direction of the measurement light.
  • the measurement light reflected on the scanning part 23 is reflected on the dichroic mirror 40 , and thereafter collected in the fundus via a dichroic mirror 91 and the objective lens 10 .
  • the measurement light reflected on the fundus passes through the objective lens 10 and the dichroic mirror 91 , and is thereafter reflected on the dichroic mirror 40 , to travel toward the OCT optical system 200 . Further, the measurement light is incident on the end 39 b of the optical fiber 38 b via the two galvanometer mirrors of the scanning part 23 , the focusing lens 24 and the collimator lens 22 . The measurement light incident on the end 39 b reaches an end 84 a of an optical fiber 38 d via the optical fiber 38 b , the fiber coupler 26 and the optical fiber 38 d.
  • an end 39 c of the optical fiber 38 c , a collimator lens 29 and the reference mirror 31 are arranged.
  • the reference mirror 31 is configured to be movable in the optical-axis direction by a reference mirror driving mechanism 50 . This allows the reference mirror 31 to change an optical path length of the reference light. That is, in this case, the reference mirror 31 is used as an optical-path-length varying member.
  • the reference light emitted from the end 39 c of the optical fiber 38 c is made to be a parallel light flux by the collimator lens 29 and reflected on the reference mirror 31 , and is thereafter collected by the collimator lens 29 , to be incident on the end 39 c of the optical fiber 38 c .
  • the reference light incident on the end 39 c reaches the coupler 26 via the optical fiber 38 c.
  • the reference light generated as described above and the fundus reflected light obtained by reflection of the measurement light on the fundus are combined in the coupler 26 , to become interference light.
  • the interference light is emitted from the end 84 a through the optical fiber 38 d.
  • a spectroscopic optical system 800 splits the interference light into each frequency component for obtaining an interference signal with reference to each frequency.
  • the spectroscopic optical system 800 has a collimator lens 80 , a grating (diffraction grating) 81 , a condenser lens 82 and a light receiving device (detector) 83 .
  • the light receiving device 83 includes a one-dimensional device (line sensor) having the sensitivity to light with a wavelength in an infrared region.
  • the light emitted from the end 84 a is made to be parallel light in the collimator lens 80 , and thereafter split in the grating 81 into each frequency component (each wavelength component).
  • the split light is then collected on the light receiving surface of the light receiving device 83 via the condenser lens 82 .
  • spectrum information with interference fringes is recorded in the light receiving device 83 .
  • the spectrum information (light receiving signal) is then input into a control part 70 .
  • the control part 70 analyzes the spectrum information by use of Fourier transformation, to measure information (A-scan signal) in the depth direction of the eye.
  • the control part 70 scans the fundus in a predetermined transverse direction with the measurement light, to obtain a tomographic image.
  • the control part 70 scans the fundus in the X-direction or the Y-direction with the measurement light, to obtain a tomographic image of the fundus in an X-Z plane or a Y-Z plane (it is to be noted that in the embodiment, such a method for one-dimensionally scanning the fundus with the measurement light to obtain a tomographic image is referred to as B-scan).
  • the obtained tomographic image is stored in a memory 72 connected to the control part 70 .
  • the control part 70 scans two-dimensionally the fundus in the XY directions with the measurement light, to obtain a three-dimensional image of the fundus.
  • an OCT image is obtained by the two galvanometer mirrors provided on the scanning part 23
  • the SLO optical system 300 is broadly divided into an illuminating optical system for illuminating the fundus and a light receiving optical system for receiving, with the light receiving device, reflected light from the fundus illuminated by the illuminating optical system.
  • the SLO optical system 300 obtains a front image of the fundus based on a light receiving signal output from the light receiving device.
  • the light emitting part 61 has a first light source (SLO light source) 61 a , a second light source (fixation optical system) 61 b , a mirror 69 , and a dichroic mirror 101 .
  • a light source which emits light with high luminance and high directivity (such as a laser diode light source or an SLD light source).
  • Infrared light emitted from the first light source 61 a passes through the dichroic mirror 101 , and travels to a beam splitter 62 through a collimator lens 65 .
  • Visible light emitted from the second light source 61 b is bent by the mirror 69 , and thereafter reflected on the dichroic mirror 101 . This visible light then travels along the same axis as that of the infrared light emitted from the first light source 61 a .
  • the first light source 61 a is used for obtaining a fundus front image for observation.
  • the second light source 61 b is used for guiding the sight direction of the eye.
  • the collimator lens 65 In the optical path for emitting laser light from the light emitting part 61 toward the eye E, the collimator lens 65 , a focusing lens 63 , the scanning part (optical scanner) 64 and the objective lens 10 are arranged.
  • the focusing lens 63 is movable in the optical-axis direction in line with a refraction error of the eye.
  • the scanning part 64 performs high-speed scanning on the fundus in the XY directions with the measurement light.
  • the scanning part 64 has a galvanometer mirror and a polygon mirror, and is driven by a scanning driving mechanism 52 . Reflected surfaces of the galvanometer mirror and the polygon mirror are arranged in a position substantially conjugate with the pupil of the eye E.
  • the beam splitter 62 is arranged between the light emitting part 61 and the focusing lens 63 . Moreover, on the reflecting direction of the beam splitter 62 , a condenser lens 66 , a confocal opening 67 and a light receiving device 68 for SLO are provided.
  • the condenser lens 66 serves to configure the confocal optical system.
  • the confocal opening 67 is arranged in a position conjugate with the fundus.
  • laser light (measurement light or fixation light) emitted from the light emitting part 61 transmits the beam splitter 62 via the collimator lens 65 , and thereafter passes through the focusing lens 63 . Subsequently, this laser light reaches the scanning part 64 .
  • the galvanometer mirror and the polygon mirror By driving of the galvanometer mirror and the polygon mirror, the reflecting direction of this laser light is changed.
  • the reflected laser light transmits the dichroic mirror 40 , and is thereafter collected in the fundus via the dichroic mirror 91 and the objective lens 10 .
  • the laser light (measurement light) reflected on the fundus passes through the objective lens 10 , the dichroic mirror 91 , the galvanometer mirror and the polygon mirror of the scanning part 64 and the focusing lens 63 , and is then reflected on the beam splitter 62 . Subsequently, this laser light is collected in the condenser lens 66 , and thereafter detected by the light receiving device 68 via the confocal opening 67 .
  • a light receiving signal generated in the light receiving device 68 is input into the control part 70 .
  • the control part 70 obtains the front image of the fundus based on the light receiving signal obtained in the light receiving device 68 .
  • the obtained front image is stored in the memory 72 .
  • the ophthalmic photographing apparatus of the embodiment has a projecting optical system 150 for projecting an alignment target to an examinee's eye.
  • This projecting optical system 150 has an infrared light source 151 , and is also arranged outside an inspection window (observation window) provided in the apparatus housing. Further, this projecting optical system 150 projects the target diagonally from the front of the eye E (the outside of the objective lens 10 in the radial direction).
  • An observing optical system 90 is provided with the objective lens 10 , the dichroic mirror 91 , an image forming lens 95 , and a two-dimensional photographing device (two-dimensional light receiving device) 97 .
  • This observing optical system 90 is arranged for photographing the eye E, to obtain the anterior-segment image.
  • the dichroic mirror 91 has a characteristic of reflecting light with a wavelength emitted from the infrared light source 151 , while being transmitted by the other light.
  • the reflected light (including alignment light) obtained by reflection of the light, emitted from the infrared light source 151 , on the anterior segment passes through the objective lens 10 and is reflected by the dichroic mirror 91 . Thereafter, the light is received by the two-dimensional photographing device 97 via the image forming lens 95 . Thereby, the two-dimensional photographing device 97 photographs the anterior-segment image. This anterior-segment image photographed by the photographing device 97 is output to the control part 70 , while being displayed on the monitor 75 .
  • control part 70 is connected to the display monitor 75 , and controls a display image thereof. Further, the control part 70 is connected with a memory (storing part) 72 , an operating part 74 for performing a variety of operations, the scanning driving mechanism 51 , the scanning driving mechanism 52 , the reference mirror driving mechanism 50 , a first driving mechanism 63 a for moving the focusing lens 63 in the optical-axis direction, a second driving mechanism 24 a for moving the focusing lens 24 in the optical-axis direction, and the like.
  • the monitor 75 two monitors, i.e., a monitor for alignment observation and a monitor for photographed image observation, may be used or one shared monitor may naturally be used.
  • the control part 70 forms a tomographic image of the fundus based on an output signal from the light receiving element 83 . Further, the control part 70 forms a front image of the fundus based on an output signal from the light receiving element 68 (refer to FIG. 2 ). The control part 70 then moves the reference mirror 31 by controlling the driving of the driving mechanism 50 . The control part 70 further controls the monitor 75 to display the obtained tomographic image within a predetermined display region (refer to FIG. 2 ).
  • the control part 70 detects the amount of positional deviation (positional deviation information) in the depth direction of the tomographic image based on an output signal from the light receiving element 68 (refer to FIGS. 3 , 4 A, and 4 B).
  • the amount of the detected positional deviation may also be detected, for example, based on the obtained tomographic image, and it may also be detected based on an A scan signal at an arbitrary scanning position before image formation.
  • the control part 70 corrects the display position of the tomographic image by controlling the display of the monitor 75 based on the detected amount of positional deviation. Thereby, the tomographic image which is obtained at any time is displayed at a predetermined position (for example, a center position C in the depth direction) within the display region of the monitor 75 (refer to FIGS. 3 and 5 ).
  • the predetermined position described above is not limited to the center position, and may be set to any arbitrary position (for example, the upper part of the display region 102 ). However, the predetermined position must be a position at which the tomographic image can be sufficiently displayed. Further, the predetermined position described above may also be changed based on an operating signal from the operating part 74 operated by the examiner.
  • control part 70 may adjust the position of the reference mirror 31 so that the amount of the detected positional deviation which is detected falls within the predetermined allowable range by controlling the driving of the driving mechanism 50 (refer to FIG. 3 ).
  • control part 70 corrects the display position of the tomographic image by controlling the display of the monitor 75 using image processing.
  • the examiner directs an examinee to gaze at a fixation light (not illustrated), and then performs alignment on the fundus.
  • a fixation light not illustrated
  • FIG. 2 when an SLO fundus image is displayed in an SLO image display region 105 on the monitor 75 , an OCT image is obtained by an OCT optical system 200 based on a predetermined scanning pattern. Thereby, the OCT image is displayed in an OCT image display region 102 on the monitor 75 .
  • control part 70 controls driving of the driving mechanism 50 based on a light receiving signal output from the light receiving device 83 , to adjust the optical path difference between the measurement light and the reference light such that the fundus tomographic image is obtained.
  • the reference mirror 31 is moved inside a predetermined movement range corresponding to the difference in ocular axial length of the examinee's eye.
  • the control part 70 moves the reference mirror 31 in a predetermined step corresponding to a photographic range in the depth direction (for example, 2 mm). The control part 70 then sets scanning lines extending in the depth direction on the images obtained at each position. Next, the control part 70 obtains the luminance distribution of the images on the scanning lines. When the luminance distribution corresponding to the fundus tomographic image (for example, a luminance distribution having an abrupt rise in luminance) has been obtained, the fundus tomographic image is displayed in the display region 102 on the monitor 75 .
  • a photographic range in the depth direction for example, 2 mm
  • control part 70 continuously corrects the display position of the image by image processing and adjusting the position of the reference mirror. Thereby, a fundus tomographic image obtained at a predetermined frame rate is constantly displayed in the center position C of the display region 102 .
  • the control part 70 detects the positional deviation of the tomographic image in the depth direction based on the obtained tomographic image. Subsequently, the control part 70 controls the display of the monitor 75 based on the detection result to display a predetermined area of the fundus tomographic image (for example, the retinal pigment epithelium) on the monitor 75 at a predetermined position (for example, the center position C).
  • a predetermined area of the fundus tomographic image for example, the retinal pigment epithelium
  • control part 70 controls the driving of the driving mechanism 50 based on the positional deviation detection result which is detected to move the reference mirror 31 . Thereby, the control part 70 adjusts the positional deviation to fall within the predetermined allowable range.
  • FIG. 3 is a flow chart for explaining the example of display position correction of the fundus tomographic image.
  • the control part 70 sets scanning lines extending in the depth direction (an A scanning direction) on the fundus tomographic image.
  • the control part 70 obtains the luminance distribution L on these scanning lines.
  • the position in the depth direction at which the luminance value is maximum (hereinafter, abbreviated to “maximum luminance value”) is detected from the luminance distribution L, and this position is set as a peak position P.
  • a reference position B is the center position in the depth direction of the tomographic image, and corresponds to the center position C in the display region 102 on the monitor 75 .
  • the control part 70 then detects a deviation amount ⁇ D between the peak position P and the reference position B of the captured image based on the obtained luminance distribution L. At this time, the detection of the deviation amount ⁇ D and the optical path length adjustment is carried out in pixel units.
  • the control part 70 determines whether the detected deviation amount ⁇ D is in a predetermined allowable range D 1 , and adjusts the optical path length based on this determination result. If the detected deviation amount ⁇ D is larger than the allowable range D 1 , the control part 70 moves the reference mirror 31 in a direction in which the deviation amount will become smaller. Thereby, the display position of the fundus tomographic image in the display region 102 is corrected. If the detected deviation amount ⁇ D is smaller than the allowable range D 1 , the control part 70 does not move the reference mirror 31 .
  • control part 70 also displays the captured fundus tomographic image on the monitor 75 in a state in which it has been moved by image processing.
  • FIGS. 4A and 4B virtually illustrate the positional relationship between the obtained tomographic image data and the display region 102 .
  • FIG. 4A illustrates the positional relationship before image processing
  • FIG. 4B illustrates the positional relationship after image processing.
  • the control part 70 moves the captured image (DL) in the direction of the reference position B by the detected deviation amount ⁇ D (refer to FIG. 4B ) to match the reference position B and the peak position P to each other.
  • the control part 70 displays the captured image after image processing in the display region 102 (refer to FIG. 5 ). In this way, even if the obtained position (peak position) of the fundus tomographic image is obtained in a state in which it is displaced from the reference position B, the display position of the fundus tomographic image is corrected so that the predetermined area of the fundus tomographic image is displayed at the center position C of the display region 102 on the monitor 75 .
  • a space S generated by the movement of the image is displayed upon attunement to the overall background color of the display image. Further, if the deviation amount is small or there is no deviation amount, the correction of the image position is not performed. In this case, the obtained fundus tomographic image is introduced into the memory 72 and then displayed on the monitor 75 as a moving image.
  • control part 70 sequentially introduces the tomographic images into the memory 72 .
  • the control part 70 performs display position correction for each single frame in a time-series to display an image after position correction on the monitor 75 .
  • image position correction is carried out continuously for each frame in the same way as the above-described correction method to display a moving image on the monitor 75 .
  • the allowable range D 1 For example, 50 pixels are set as the allowable range D 1 . This corresponds to 1/10 of an image data set to 512 ⁇ 512 pixels. Further, a maximum movement distance of the reference mirror 31 while obtaining a fundus tomographic image of one frame may be set to D 2 (for example, approximately 10 pixels).
  • D 2 for example, approximately 10 pixels.
  • the control part 70 gradually moves the position of the tomographic image over several frames while moving it by D 2 in each single frame. If the deviation amount from the limit position of the allowable range D 1 is smaller than D 2 , then the control part 70 moves the position of the tomographic image by the detected deviation amount ⁇ D in each single frame.
  • a desired scanning position/pattern is set by the examiner, and a predetermined trigger signal is output. Accordingly, the control part 70 obtains a tomographic image based on the set scanning position/pattern, and stores the obtained image data in the memory 72 . Further, at this time, the control part 70 stores a fundus front image obtained by the SLO optical system 300 in the memory 72 .
  • the control part 70 corrects the display position of the tomographic image by image processing in each frame. Thereby, shaking of the tomographic image resulted from breathing or a slight quiver of the body can be suppressed. Therefore, a tomographic moving image can be stably displayed at a predetermined display position. Further, blurring of the tomographic image resulted from vibrations of a motor can also be avoided. Thus, even if the examinee's eye moves, the fundus tomographic image on the monitor 75 will appear with no shaking and no movement from the predetermined position.
  • the control part 70 moves the reference mirror so that the amount of the detected positional deviation falls within the predetermined allowable range.
  • a large positional deviation of the fundus of the examinee's eye can be handled.
  • the tomographic image will not deviate from the display screen. Therefore, the trouble required for readjusting the optical path length can be avoided.
  • the tomographic image can be displayed at a nearly constant sensitivity by moving the reference mirror.
  • the setting of the allowable range D 1 will be explained below. Complication may arise because the reference mirror 31 must be constantly moved in order to completely eliminate the deviation amount by adjusting the optical path length. Therefore, by setting the predetermined allowable range D 1 , continuous movement of the reference mirror is prevented.
  • the predetermined allowable range D 1 is preferably larger than a comparatively small amount of positional deviation corresponding to micromotion of the tomographic image resulted from fluctuations in the interference light, noise, breathing of the examinee, and the like, and smaller than a positional deviation exceeding the comparatively small amount of positional deviation (for example, a positional deviation generated when the forehead moves relative to the forehead pad).
  • the predetermined allowable range D 1 may also be a range which is larger than a comparatively small amount of positional deviation at which the entire tomographic image can be sufficiently observed even if the tomographic image deviates from the predetermined position, and smaller than a positional deviation exceeding the comparatively small amount of positional deviation.
  • the predetermined allowable range D 1 may also be a range corresponding to a large amount of positional deviation at which the fundus tomographic image deviates from the display region 102 .
  • the reference mirror 31 is moved only when this kind of large amount of positional deviation is detected.
  • control part 70 may also simultaneously correct the display position of the tomographic image by controlling the display of the monitor 75 and adjust the position of the reference mirror 31 by controlling the driving of the driving mechanism 50 .
  • control part 70 may also adjust the position of the tomographic image by only controlling the display of the monitor 75 using image processing without moving the reference mirror 31 , without consideration to the amount of the detected positional deviation of the tomographic image.
  • the adjustment of the optical path length was carried out automatically until a fundus tomographic image is first obtained.
  • the embodiment is not limited to this configuration, and the optical path length may be adjusted based on an operation by the examiner viewing the monitor 75 .
  • the optical path length may be adjusted based on an operation by the examiner viewing the monitor 75 .
  • the tomographic image when correcting the position of the tomographic image by image processing, the tomographic image is moved to a predetermined display region.
  • the embodiment is not limited to this configuration, and, for example, an extracted region of an image which is output to the predetermined display region in the image data of the tomographic image may also be changed.
  • a method in which the deviation between the peak value and the reference position in accordance with the luminance distribution is detected to detect the positional deviation.
  • various image processing methods can be used (a method using various correlation functions, a method utilizing Fourier transform, a method based on matching of characteristic points).
  • a tomographic image in which there is no positional deviation is set as a reference image, and the amount of the detected positional deviation relative to the reference image is calculated.
  • an optical-path-length varying member is provided in the optical path of the reference light.
  • the embodiment is not limited to this configuration, and the optical-path-length varying member may also be provided in the optical path of the measurement light.
  • the collimator lens 22 and the end of the optical fiber 39 b are moved in the optical axis direction.
  • an aspect of the invention is applied to a fundus photographing apparatus, which is one example of an ophthalmic photographing apparatus.
  • the embodiment is not limited to this configuration, and it is also possible to apply the aspect of the invention to an ophthalmic photographing apparatus for photographing a tomographic image of a predetermined area of an examinee's eye (for example, an anterior segment tomographic image) using an optical interference optical system formed by applying the OCT principle.
  • the aspect of the invention is not applied only to ophthalmic photographing apparatuses.
  • the aspect of the invention is also applicable to an optical tomographic image photographing apparatus for photographing a tomographic image of an organism other than the eye (for example, skin and veins), an object other than an organism, or the like.
  • the ophthalmic photographing apparatus in accordance with the embodiment may also have a configuration for tracking a measurement light scanned on an object relative to the object.
  • a frontal optical system that obtains a front image of an object can be used.
  • the control part 70 detects a deviation of the scanning position on the object with respect to the XY directions at any time based on the front image obtained by the frontal optical system.
  • the control part 70 then corrects the deviation in the scanning position by controlling an optical scanner (for example, the scanning part 23 ) to correct the scanning position of the measurement light.
  • the control part 70 detects by image processing a positional deviation between front images obtained at any time.
  • various image processing methods can be used (a method using various correlation functions, a method utilizing Fourier transform, a method based on matching of characteristic points).
  • a tomographic image in which there is no positional deviation is set as a reference image, and the amount of the detected positional deviation relative to the reference image is calculated.
  • an optical system for obtaining a front image of an object for example, an SLO optical system or a CCD camera can be used. Further, a front image is obtained by an interference optical system (for example, the OCT optical system 200 ).
  • the control part 70 scans the measurement light in two dimensions using an optical scanner (for example, the scanning part 23 ). The control part 70 then obtains a front image based on a light receiving signal output from a detector (for example, the light receiving element 83 ). For example, an integrated value of spectral data at each position in the X direction and the Y direction is used as the luminance value of the image.
  • control part 70 moves the optical-path-length varying member (the reference mirror 31 ) by controlling the driving of the driving mechanism 50 , and thereby mechanically corrects the display position of the tomographic image.
  • control part may also control the driving of a driving part for mechanically correcting the display position of the tomographic image which is not limited to the driving mechanism 50 .
  • a moving unit 6 for moving the entire interference optical system 200 relative to the object is cited.
  • the control part 70 adjusts the position of the entire interference optical system by controlling the moving unit 6 .
  • the control part 70 may also control the driving of an observation optical system 90 as a configuration for detecting movement of the eye. Further, in this case, the control part may also control the driving of both the moving unit 6 and the driving mechanism 50 as a mechanical driving part.

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